Field of the Invention
The present invention relates to the art of a heat pipe having a wick structure constructed of sintered metal powder arranged in a sealed container.
Discussion of the Related Art
Conventional heat pipes are adapted to absorb heat from a heat generating object such as an electronic device in the form of latent heat of working fluid. In the heat pipe, the working fluid is evaporated by an external heat and condensed while radiating heat. Cooling performance of the heat pipe of this kind may be enhanced by increasing mass flow of the working fluid.
In recent years, electronic devices has been downsized and highly improved hence generate higher heat. Therefore, the heat pipes are required to be downsized while enhancing heat transport capacity. For example, given that a flat heat pipe and a cylindrical heat pipe have same widths, the flat heat pipe is thinner than the cylindrical heat pipe. However, an inner space of the flat heat pipe serving as a flow path is smaller than that of the cylindrical heat pipe.
For instance, US2012/0118537 A describes a flattened heat pipe comprising a wick structure attached to an inner flat wall of a container, and vapor flowing passages formed in curves areas of both sides of the container. Working fluid is encapsulated and circulates in the container.
US2011/0303392 A also describes a flat heat pipe comprising a wick formed by bundling a plurality of thin metal wires extending in a longitudinal direction of a container while being contacted to a predetermined portion of an inner face of the container.
In turn, JP-A-2013-2640 describes a wick structure comprising a fiber wick layer formed of a plurality of metal wires laid on an inner surface of a sealed container, and a powder wick layer laid on the fiber wick layer.
Further, JP-A-11-294980 describes a cylindrical heat pipe having a wick structure for increasing a mass flow of the working fluid flowing through a flow path from a condensing portion toward an evaporating portion.
Specifically, according to the teachings of JP-A-11-294980, the wick structure is comprised of a metal net and a sintered metal powder. An inner wall of a container is entirely covered with the metal powder, and the metal net is situated on the metal net or interposed between the container and the metal powder.
However, according to the heat pipe taught by US2012/0118537 A, a pressure loss of the wick structure may be high, and hence it may be difficult to transport the working fluid over a long distance. Although a traveling distance of the working fluid can be extended by the wick taught by US2011/0303392 A, a flow rate of the working fluid per unit of area has to be increased. According to the wick structure taught by JP-A-2013-2640, thermal resistance between the container and the wick may be too large and hence the metal powder may fall from the wick into grooves. According to the wick structure taught by JP-A-11-294980, the sintered metal powder may not be fixed to the metal net firmly thereby increasing thermal resistance.
The present invention has been conceived noting the foregoing technical problems, and it is therefore an object of the present invention is to enhance the heat transfer performance of a heat pipe by efficiently returning working fluid flowing through a wick structure arranged in a sealed container.